Installing solar PV at your school will reduce the electricity you consume from the national grid, and reduce your school's carbon emissions. Your PTA might be prepared to help you raise some of the cost of installing the panels.
The estimates in the table assume you have roof space and that is it roughly south facing - as this is best for schools whose peak demand is during the middle of the day when south facing panels produce the most electricity.
The benefits of solar PV will be reduced if you make your school more energy efficient. However, if you want your school to reduce its carbon emissions you should consider both installing solar panels and reducing your electricity consumption.